Styrene polymerization initiated by sodium and promoter



Jan. 5, 1960 R. w. MYERHOLTZ, JR., -ETAL 2,920,065

STYRENE POLYMERIZATION INIT-IATED BY SODIUM AND PROMOTER Filed Feb. 28,1957 m. m5 N .Q6 .m10 QG mib NG OG .v6 I h6 .si uw l u. uw l e sv EES hmS [Il] [Lisons/,1 alsa/14W INVENTORS: Ralph H. Myer/l0/fz,./r.

Dona/d E. Burney STYRENE POLYMERIZATION INITIATED BY SODIUM AND PROMOTERRalpnw. Myerholfz, Jr., Highland, and Donald E. Burrr'llibago, lll., acorporation of Indiana Application February 28, 1957, Serial No. 643,025

11 Claims. (Cl. 260-935) This invention relates to an improved styrenepolymerization process wherein styrene is polymerized from a solutionthereof in an aromatic or saturated hydrocarbon solvent with a catalyticamount of dispersed sodium to serve as a reaction initiator, and itpertains more particularly to modifying the polymerization by the use ofminute amounts of a substance which is herein referred to as a promoter.

It is known that styrene may be' polymerized from a solution thereof ina non-polymerizable hydrocarbon solvent such as Xylene, ethylbenzene,toluene, benzene, or a mixture thereof by use of about .1 to .6 percentby weight, based on styrene, of sodium which is finely dispersed so thatit has a particle size of about 1 to 100 microns. Thus, at 100 C.,polymers having an intrinsic viscosity of about 0.1 were obtained whileat 60 C. a

' polymer having an intrinsic Viscosity of the order of 1 was obtained.

An object of our invention is to provide an improvement on thispolymerization technique. A further object is to obtain a highermolecular weight polymer at a given temperature with smaller amounts ofcatalyst than have heretofore been required. An important object is tocontrol the polymerizationl reaction rate so that close polymerizationtemperature control is possible. Another Vobjective is to produce apolymer having a more uniform molecular Weight and more desirableproperties than have heretofore been obtained. Other objects will beapparent from the following detailed description.

We have discovered that dihydric alcohol-dialkyl ethers Griliith, Ind.,assignors to Standard Oil Company,-

, United States Patent it' 2,920,065 l fatented Jan. 5, 1960 icepolymerization at 60 C. for 60 minutes for a 20 volume z percentsolution of stryrene in xylene.

. line.

To demonstrate the effect of amounts of our promoter' in styrenepolymerization, a series of reactions were cardispersion of sodium inxylene in the form of particles about 10 to 20 microns in size; thecatalyst or initiator is thus usually prepared as a concentrateddispersion which may be diluted with xylene' or other'- diluent prior toactual use. The promoter was diethylene glycol dimethyl ether which wasredistilled from sodium prior to use. Generally the promoterxand sodiumwere mixed just prior to addition to the lreaction mixture, butequivalent results may be obtained by adding the promoter to thepolymerization feed and then adding the sodium y1 alone, after reactiontemperature has been reached. Prior to addition of the initiator, thepressure was reduced to the point which caused the reaction mixture toboil at the desired reaction temperature which inthis case was 60"` C.After catalyst addition there was an induction period 1 which variedwith sodium concentration, promoterfconor ethylene glycol dialkylethers, such as ethylene glycol dimethyl ether, diethylene glycoldimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycoldimethyl ether, or the like, have a remarkable promoting effect instyrene polymerization when employed with dispersed sodium in sucientlysmall amounts, preferably :..1

product quality. On the other hand, the use of at least .01 andpreferably at least .03 weight percent of the dened promoter enables thepolymerization to be effected with lesser amounts of sodium thanheretofore required, produces a much higher molecular weight productthan is obtainable under like conditions in the absence of promoter andresults in a nal product of greater uniformity and superior properties.Dispersed sodium is used in effective concentrations in the range ofabout 0.01 to about 0.5 percent by weight based on monomer. Q,

The invention will be more clearly understood from the followingdetailed description of preferred examples read in conjunction with vtheaccompanying drawing which is a chart graphically showing vthe 'ellectof indicated amounts of promoter on sodium initiated styrene centration,etc. and the induction period was followed by a period of vigorousreaction usually lasting about 1 to 20 minutes or more; each test wascontinued for 60lto minutes after the beginning of vigorous reaction.After the run, an aliquot of the resulting polymer solution vwas dilutedwith benzene and precipitated by addition of methanol. Conversion andintrinsic viscosities were determined on the dried polymer, intrinsicviscosities being measured in benzene atl 30 C. and expressed indeciliters per gram. v Y j The lirst series of tests was made with .025percent sodium based on monomer at '60 C. for a vreaction period of 90minutes with the following results:

Percent: *n Percent Promoter Conversion (90 minute reaction period)amount'ofpromoter shouldfbe of the order of about .05I

weight percent based on monomer.

The next three series of tests were made with .05 percent sodium, 0.10percent sodium and 0.2 percent sodium at 60 C. for 60 minutes withresults shown in the fol- The catalyst was a 50 weight percent- .1sodium Percent n Percent Promoter Conversion 0.01 1. 04 89 0. 025 1. 6096 0. O5 1. 63 96 0. 10 1'. 44 93 0.20 1. 37 86 0. 40 1. 20 97 (60minute reaction period) .2 sodzum Percent n Percent PromoterConversion 1. (60 minute reaction period) The foregoing data, as shownby the annexed drawing, show that the intrinsic viscosities of thepolymer increase at a very great rate up to about .03 weight percentpromoter while the curve tends to level off at amounts of promoter inthe range of about .2 to .5 weight percent. Under the conditions of theforegoing tests, amounts of promoter larger than .5 weight percentresulted in a reaction rate which was'too rapid for practical control.However, with different concentrations of styrene in solvent which mayrange from about to 40 percent and with different polymerizationtemperatures which maybe in the range of 20 to 100 or 150 C. but areusually at least 40 but below about 80 C., the amounts of promoter willlie within the range of about .01 to 1 weight percent based on monomerand usually in the lower part of this range. Preferably the amount ofpromoter is less than the amount of sodium on a mol basis.

In another series of tests a 20 percentl solution of styrene in m-xylenewas polymerized at 58 C. for 65 minutes (after start of polymerization)in a series of tests made in the manner substantially as hereinabovedescribed, in order to compare the effectiveness of a conventionaldispersed sodium catalyst and a sodium dispersion promoted with1,2-dimethoxyethane (ethylene glycol dimethyl ether). The promoteddispersion was prepared by adding 1.2 ml. of a 50 percent dispersion ofsodium in p-xylene to a mixture of 3 ml. of m-xylene and 12.5 ml. of1,2-dimethoxyethane. The sodium particles turned from gray to a lighttan. This mixture was thoroughly agitated and then ml.`was withdrawn anddiluted by adding to 100 ml. of m-xylene. Portions of the dilutedmixture were used for polymerizations for comparison withpolymerizations made with like` amounts of unpromoted dispersed sodiumwith the following results:

From the foregoing data it is apparent that the promoted sodiumdispersion gives a higher yield of polymer of higher intrinsic viscosityand in a shorter length of time than does an unpromoted sodiumdispersion.

The rst series of tests hereinabove s et forth employed diethyleneglycol dimethyl ether while the latter tests employed monoethyleneglycol dimethyl ether. Tetraethylene glycol dimethyl ether (0.5 weightpercent based on styrene) was employed with .1 weight percent sodium,also based on styrene, in polymerizing styrene from a 20 percentsolution thereof in xylene; polymerization started at 60 C. after a 4minute induction period and polymerization was very rapid, causing thetemperature to rise to C., the product in this case having an intrinsicviscosity of 1.12. These are simply examples of dihydric alcohol-dialkylethers or of an ethylene glycol-dialkyl ether. Although the alkyl groupsin the dialkyl ether may each have 1 to 4 carbon atoms, at least one ofthem is preferably a methyl group; diethyl ethers appear to be lesssatisfactory than dimethyl ethers. The preferred ethylene glycoldimethyl ethers may be represented by the formula CH3(OCH2CH2)OCH3 wherenis a whole number which is preferably not higher than about 20.

While dispersed sodium has been described as the catalyst, it will beunderstood that other dispersed alkali metals or alloys of alkali metalsmay be used instead of sodium provided that they exhibit the requiredcatalytic activity; these other alkali metals or alloys thereof are not,however, known to be equivalents of sodium.

Styrene itself was polymerized in the foregoing 4examples, but it shouldbe understood that other vinyl monomers such as alpha methyl styrene andthe like may be used instead of or in admixture with simple sytrene. Asabove indicated, the monomer is preferably polymerized from a solutionthereof in a non-polymerizable hydrocarbon which may be a. parafiinichydrocarbon such as hexane, pentane or the like, a naphthenichydrocarbon such as cyclopentane or cyclohexane but which is preferablyva low boiling aromatic hydrocarbon such as benzene,

toluene, xylene or a mixture thereof.

While we do not wish to be bound by 'any theory of the mechanism of thereaction or the manner in which our improved promoter functions, itappears that the rst step in sodium-initiated polymerization of styreneis the formation of a sodium-styrene adduct. This adduct thendissociates into a sodium ion and a styrene ion radical. The latter isprobably the species responsible for the `initiation of polymerization.Compounds such as diethylene glycol dimethyl ether should be ,capable offorming a complex with sodium ions. This would favor dissociation of theadduct and would lead to `an increase in polymerization rate. Excessiveamounts of Athe promoter would lead to a decrease in polymer molecularweight since ,it would cause the formation of more Vinitiator molecules.The complexed sodium ion would be quite bulky; with the proper amount ofpromoter termination will be delayed, leading to a higher molecularweight than obtained with sodium alone. These promoters may alsofunction by complexing impurities which would cause.

[nl Percent Percent Promoter N a 60 C. 70 C. 79 C 0.05 0. 10 1. 63 1.250.05 0.20 1. 44 l. 12 0.10 0. 10 1. 44 1. 20 0. S2 O. l0 0. 20 1. 39 1.09 0. 20 0. 05 1. 46 O. 84

(60 minute reaction period) aoaope From the foregoing detaileddescription it will be seen that the objects of our invention have beenattained. While these tests were carried out batch-wise, it iscontemplated that polymerization may be carried out in a continuousmanner. The catalyst, promoter and solvent may be removed from thepolystyrene in manners known to those skilled in the art. By thistechnique a polystyrene can be produced with properties equivalent orsuperior to the properties of commercial styrene polymer heretoforeproduced.

We claim:

1. The method of polymerizing a vinyl monomer consisting essentially ofan aromatic hydrocarbon selected from the group consisting of styreneand alpha-methylstyrene from a solution thereof in a non-polymerizablehydrocarbon solvent at a temperature in the range of 20 to 100 C. withan effective amount of a dispersed sodium in the range of about 0.01r toabout 0.5 percent by weight, based on said monomer, to serve as apolymerization initiator, which method comprises etecting thepolymerization in contact with at least about .01 weight percent butless than 1.0 weight percent based on said vinyl monomer of a dihydricalcohol-dialkyl ether wherein the alkyl groups contain not more than 4carbon atoms.

2'. 'Ihe method of polymerizing a vinyl monomer consisting essentiallyof styrene from a solution thereof in a non-polymerizable hydrocarbonsolvent at a temperature sisting essentially of styrene from a 5 to 40percent solution thereofin a hydrocarbon solvent at a temperature above40 but below 80 C. with a dispersed sodium catalyst, which methodcomprises electing the polymerization with an amount of dispersed sodiumcatalyst in the range of .01 to .5 weight percent and an amount of anethylene glycol dimethyl ether in the range of .0l to .5

percent by weight, each percentage being based on styrene monomer, andrecovering a polymer of styrene having an intrinsic viscosity of atleast about 0.8 deciliter per gram in benzene solution at 30 C.

7.Y The method of claim 6 wherein the amounts of said Y sodium and saidether respectively do not exceed about in the range of 20 to 100 C. withan elective amount of dispersed sodium polymerization initiator in therange of about 0.01 to about 0.5 percent by weight, based on styrenemonomer, which method comprises eecting the polymerization in contactwith at least about 0.01 weight percent but less than 1.0 weight percentbased on styrene monomer of an ethylene glycol dialkyl ether in whichthe respective alkyl groups have 1 to 4 carbon atoms, inclusive, andrecovering a polymer of styrene having an in- .2 weight percent.

8. The method of claim 6 wherein said ether is diethylene glycoldimethyl ether and less than 1 mol of said ether is employed per gramatom of sodium.

k9. The process of claim 1 wherein said hydrocarbon solvent is a lowboiling aromatic hydrocarbon.

10. The process of claim llwherein said hydrocarbon solvent is a paranichydrocarbon.

11. The process of claim l wherein said vinyl monomer 2,327,082 WalkerAug. 17, 1943

1. THE METHOD OF POLYMERIZING A VINYL MONOMER CONSISTING ESSENTIALLY OFAN AROMATIC HYDROCARBON SELECTED FROM THE GROUP CONSISTING OF STYRENEAND ALPHA-METHYLSTYRENE FROM A SOLUTION THEREOF IN A NON-POLYMERIZABLEHYDROCARBON SOLVENT AT A TEMPERATURE IN THE RANGE OF 20 TO 100* C. WITHAN EFFECTIVE AMOUNT OF A DISPERSED SODUIM IN THE RANGE OF ABOUT 0.01 TOABOUT 0.5 PERCENT BY WEIGHT, BASED ON SAID MONOMER, TO SERVE AS APOLYMERIZATION INITIATOR, WHICH METHOD COMPRISES EFFECTING THEPOLYMERIZATION IN CONTACT WITH AT LEAST ABOUT 901 WEIGHT PERCENT BUTLESS THAN 1.0 WEIGHT PERCENT BASED ON SAID VINYL MONOMER OF A DIHYDRICALCOHOL-DIALKYL ETHER WHEREIN THE ALKYL GROUPS CONTAIN NOT MORE THAN 4CARBON ATOMS.